When taking off from Cologne EDDK recently, I was asked by ATC if I can accept taking off from about halfway down the runway – obviously to shorten my taxi ways and to optimize overall operations. I accepted and was issued a revised taxi clearance (initially they had cleared to the “regular” holding point at the beginning of the runway.
When this happened to me previously and I wasn’t as accustomed to large airports yet (and also once at EDDH when I was asked if I can accept a cross-wind take-off, where an into wind runway was available, too) I rejected because I was too focused on getting everything right and I didn’t want to accept ad-hoc changes.
Generally, how to you consider such requests? Obviously, on a large airport, you can more then easily take-off from the various runway holding points, even beyond half-way. It is however, while you’re already taxiing, ultimately guesswork, because you’re not going to perform a proper take-off distance calculation before responding. Of course, if you had done that calculation during the pre-flight planning, you would only need to know the TORA of the intersection being offered and ATC could give that to you if you requested it. But realistically, I don’t do that calculation when planning to take off from a 3000 meter concrete runway at normal altitude.
Now, while such a take-off is most likely not going to be a problem from a take-off distance point of view, you are in fact giving up a safety margin in case of an EFATO. A safety margin you don’t have at smaller airfields in the first place – but it’s a nice thing to have at large runways to be able to land back on it more likely than not if you have an immediate emergency right after take-off.
I would take the view that if you can accept something that is safe to help ATC out, then especially at somewhere busy like Cologne, you do so. Airliners frequently plan intersection takeoffs to save taxi time &c, and the form is to advise ATC on taxi – " xxx request taxi, able Bravo"
I appreciate there is a big psychological difference between departing from 1000m of Tarmac, and departing with 1000m remaining of a 2000m runway, but if your performance numbers allow it, I would go for it. It’s worth having some canned performance numbers to hand for MTOW, ISA+10 to hand, or simply knowing the figure for your aircraft and deciding what the minimum you are prepared to accept will be. It may also depend on the obstacles around the airfield – an intersection takeoff at an airport with fields around might be fine, but somewhere surrounded by buildings you might prefer a full length departure to gain maximum height over the upwind threshold. You should bear in mind that finding a gap for you to do a full length takeoff may be difficult as approach will vector aircraft with 5nm spacing in final, which gives a gap long enough for typical jet/TP departures, but potentially not enough time for safe separation for an SEP.
The trick is to do it beforehand, but one only tends to learn it after someone has asked you the first time! However, what you are comfortable with is ultimately up to you.
Patrick wrote:
But realistically, I don’t do that calculation when planning to take off from a 3000 meter concrete runway at normal altitude.
I can recommend Autorouter, which does the calculation for you if you entered the data in the first place.
I have never been offered intersection takeoffs with less than say 1200m TORA, and my ground roll is less than 300m, so for me this is adequate margin.
Patrick wrote:
hile you’re already taxiing, ultimately guesswork, because you’re not going to perform a proper take-off distance calculation before responding
well, i might be oversimplifying but how detailed take-off calculation are you performing? if the runway is 1000+ m and concrete – this is fine for almost any single engine aircraft – at least those I do fly. If SR20 or P2010 on a full weight the threshold will lift a bit. But ATC will be unlikely to offer you anything shorter anyway unless you ask for.
Airport surroundings is a factor as well. Good point on taking off from threshold you can reduce max power into climb setting sooner than 500 ft – if engine is to fail you still have enough concrete to land on.
We should be aware that at such a big airport we can be a bit of a nuisance to the normal users, both ATC and pilots. We should do everything we can to minimise their annoyance – within the limits of safety. I also think some controllers might not take into account our (planes’) limitations, being perhaps little used to them; so some of their suggestions/instructions might be questionable. I am sure they will accept a reasonable polite objection.
Most larger airports with frequent GA traffic have standard intersections for small airplanes. They line up the airliners at the beginning of the runway, the GA aircraft somewhere further down and then squeeze them in as traffic permits.
I have about 100 takeoffs in EDDS Stuttgart and I believe not one of them was from intersection A. My homebase has 750m, why should I be concerned if a large airport offers me 2000m instead of 2400m?
I would accept provided I have at least the required ASDA.
Another way to look at it is that you may want to have at least TODR+LDR so you can climb to 50’ and still be able to land again in case of engine failure.
Yet another way to look at it is that you always want the full length of the runway, but if it means taxing 3 km, you will eventually want to revisit that view 
I think intersection takeoffs are less stressful than when you are orbiting end of downwind and slotted in at the last minute on a high key approach between fast jet traffic and told to expedite as there is a 777 heavy barrelling down the ILS behind you….
I’d rather have the heavy behind me (not too near, though) then before me – wake turbulence is just as invisible.
Indeed I think I’d prefer a long waiting time over being squeezed between two airliners.
If you want Maximum Safety: Always use whole length of runway
But: I would accept it too, because if I take off from 500 m runways all the time, why should I not acept 2000?
